package chapt17networkProgram;

import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class DownUtil {
    //定义下载资源的路径
    private String path;
    //指定所下载的文件的保存位置
    private String targetFile;
    //定义需要多少个线程下载资源
    private int threadNum;
    //定义下载的线程对象
    private DownThread[] threads;
    //定义下载的文件总大小
    private int fileSize;

    public DownUtil(String path, String targetFile, int threadNum){
        this.path = path;
        this.targetFile = targetFile;
        this.threadNum = threadNum;
        //初始化threads数组
        threads = new DownThread[threadNum];
    }
    public void download() throws Exception{
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(5 * 1000);
        /*原代码，因403，不可用 */
//        conn.setRequestMethod("GET");
//        conn.setRequestProperty("Accept",
//                "image/jpg, image/gif, image/jpeg, image/pjpeg, image/pjpeg, " +
//                        "application/x-shockwave-flash, application/xaml+xml, " +
//                        "application/vnd.ms-xpsdocument, application/x-ms-xbap, " +
//                        "application/x-ms-application, application/vnd.ms-excel, " +
//                        "application/vnd.ms-powerpoint, application/msword, */*");
//        conn.setRequestProperty("Accept-Language", "zh-CN");
//        conn.setRequestProperty("Charset", "UTF-8");
//        conn.setRequestProperty("Connection", "Keep-Alive");

        conn.setRequestMethod("GET");
        conn.setRequestProperty("referrer-Policy", "strict-origin-when-cross-origin");
        conn.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7");
        conn.setRequestProperty("Accept-Encoding", "gzip, deflate, br, zstd");
        conn.setRequestProperty("Accept-Language", "zh-CN,zh;q=0.9");
        conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36");


        //得到文件大小
        fileSize = conn.getContentLength();
        conn.disconnect();
        int currentPartSize = fileSize / threadNum + 1;
        RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
        //设置本地文件的大小
        file.setLength(fileSize);
        file.close();
        for (int i = 0; i < threadNum; i++) {
            //计算每个线程下载的开始位置
            int startPos = i * currentPartSize;
            //每个线程使用一个RandomAccessFile进行下载
            RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");
            //定位该线程的下载位置
            currentPart.seek(startPos);
            //创建下载线程
            threads[i] = new DownThread(startPos, currentPartSize, currentPart);
            //启动下载线程
            threads[i].start();
        }
    }
    //获取下载的完成百分比
    public double getCompleteRate(){
        //统计多个线程已经下载的总大小
        int sumSize = 0;
        for (int i = 0; i < threadNum; i++) {
            sumSize += threads[i].length;
        }
        //返回已经完成的百分比
        return sumSize * 1.0 / fileSize;
    }

    private class DownThread extends Thread{
        //当前线程的下载位置
        private int startPos;
        //定义当前线程负责下载的文件大小
        private int currentPartSize;
        //当前线程需要下载的文件块
        private RandomAccessFile currentPart;
        //定义该线程已下载的字节数
        public int length;
        public DownThread(int startPos, int currentPartSize,RandomAccessFile currentPart){
            this.startPos = startPos;
            this.currentPartSize = currentPartSize;
            this.currentPart = currentPart;
        }
        public void run(){
            try {
                URL url = new URL(path);

                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setConnectTimeout(5 * 1000);
//                conn.setRequestMethod("GET");
//                conn.setRequestProperty("Accept",
//                        "image/jpg, image/gif, image/jpeg, image/pjpeg, image/pjpeg, " +
//                                "application/x-shockwave-flash, application/xaml+xml, " +
//                                "application/vnd.ms-xpsdocument, application/x-ms-xbap, " +
//                                "application/x-ms-application, application/vnd.ms-excel, " +
//                                "application/vnd.ms-powerpoint, application/msword, */*");
//                conn.setRequestProperty("Accept-Language", "zh-CN");
//                conn.setRequestProperty("Charset", "UTF-8");

//                Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36
//                Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36
                conn.setRequestMethod("GET");
                conn.setRequestProperty("referrer-Policy", "strict-origin-when-cross-origin");
                conn.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7");
                conn.setRequestProperty("Accept-Encoding", "gzip, deflate, br, zstd");
                conn.setRequestProperty("Accept-Language", "zh-CN,zh;q=0.9");
                conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36");
                conn.setRequestProperty("Connection", "keep-Alive");
                InputStream inStream = conn.getInputStream();
                //跳过startPos个字节，表明该线程只下载自己负责的那部分文件
                inStream.skip(this.startPos);
                byte[] buffer = new byte[1024];
                int hasRead = 0;
                //读取网络数据，并写入本地文件
                while (length < currentPartSize && (hasRead = inStream.read(buffer)) != -1){
                    currentPart.write(buffer, 0, hasRead);
                    //累计该线程下载的总大小
                    length += hasRead;
                }
            } catch (MalformedURLException e) {
                System.out.println("url 格式化异常");
                e.printStackTrace();
            } catch (IOException e) {
                System.out.println("IO 流异常");
                e.printStackTrace();
            }
        }
    }
}
